Since most of the conventional power supply systems are designed according to the designed specifications of the load terminal, the output power that can be provided by a power supply system is a preset value. The output power must be so set that electric power sufficient for the load terminal to work normally, i.e. the maximum power consumption at the load terminal, can be provided in any condition. And, when viewing from the aspect of practical application, a load terminal of a computer system or an electronic device, such as the central processing unit (CPU), the random access memory (RAM), the display, etc., would not always in a full-load state.
Among others, the electronic devices for mobile communication are generally in a standby or power-saving mode in most time. Therefore, in practical application, it is very important for the power supply system to well match the power level needed by the load terminal.
In a conventional notebook computer, the power supply system thereof uses a rectifier transformer to convert alternating current (AC) into direct current (DC), which is then directly sent to the computer system of the notebook computer. Part of the DC power received by the computer system is used to charge the battery in the notebook computer. When the transformer loses its AC power supply, the battery can provide the power needed by the computer system to work normally.
However, the conventional power supply systems can use only one of the transformer and the battery to supply the power each time. That is, the conventional power supply systems are not designed to allow the transformer and the battery to supply power to a computer system or an electronic device at the same time. Thus, the electric power usable by the computer system or the electronic device is restricted to the specifications set for the transformer and the battery. Electric power exceeding the specifications set for the transformer and the battery is not usable by the computer system or electronic device.